Enhanced nutrient supply promotes mutualistic interactions between cyanobacteria and bacteria in oligotrophic ocean.

Cyanobacteria can form complex interactions with heterotrophic microorganisms, but this relationship is susceptible to nutrient concentrations. Disentangling the cyanobacteria-bacteria interactions in relation to nutrient supply is essential to understanding their roles in geochemical cycles under global change. We hypothesize that enhanced nutrient supply in oligotrophic oceans can promote interactions among cyanobacteria and bacteria. Therefore, we investigated the planktonic bacteria and their interactions with cyanobacteria in relation to elevated nutrients caused by enhanced upwelling around a shallow and a deep seamount in the tropical western Pacific Ocean. We found obviously higher complexity of network occurred with significantly more cyanobacteria in the deep chlorophyll maximum layer of the shallow seamount when compared with that of the deep seamount. Cyanobacteria can shape bacterial interaction and community evenness in response to relatively high nutrient concentrations. The effects of the nutrients on cyanobacteria-related networks were further estimated based on the Tara Oceans data. Statistical analyses further showed a facilitative effect of nitrate concentrations on cyanobacteria-bacteria mutualistic interactions in the global oligotrophic ocean. By analysing the Tara Ocean macrogenomic data, we detected functional genes related to cyanobacteria-bacteria interactions in all samples, indicating the existence of a mutualistic relationship. Our results reveal cyanobacteria-bacteria interaction in response to nutrient elevation in oligotrophic ocean and highlight the potentially negative effects of global change on the bacterial community from the view of the bio-interaction.

Secondary metabolites with fungicide potentials from the deep-sea seamount-derived fungus Talaromyces scorteus AS-242.

Marine natural products play an important role in biopesticides. Seven new secondary metabolites with different structural classes, including two cycloheptapeptides, scortide A (1) and scortide B (2), two 19-nor-diterpenoids, talascortene H (3) and talascortene I (4), two diterpenoid acids, talascortene J (5) and talascortene K (6), and one triterpenoid, talascortene L (7) were isolated and identified from the sea-anemone-derived endozoic fungus Talaromyces scorteus AS-242. Their structures were comprehensively assigned by spectroscopic data analysis, single-crystal X-ray diffraction, tandem mass spectrometry, and electronic circular dichroism (ECD) calculations. The result of the antimicrobial assay demonstrated that compounds 1 - 6 have inhibitory activity against several human, aquatic, and plant pathogens with minimum inhibitory concentration (MIC) values ranging from 1 to 64 µg/mL. Specially, compounds 2 and 4 showed significant activities against the pathogenic fungus Curvularia spicifera with the MIC value of 1 µg/mL, providing an experimental basis of 2 and 4 with the potential as lead compounds to be developed into biopesticides.

Stochastic and Deterministic Assembly Processes in Seamount Microbial Communities.

Seamounts are ubiquitous in the ocean. However, little is known about how seamount habitat features influence the local microbial community. In this study, the microbial populations of sediment cores from sampling depths of 0.1 to 35 cm from 10 seamount summit sites with a water depth of 1,850 to 3,827 m across the South China Sea (SCS) Basin were analyzed. Compared with nonseamount ecosystems, isolated seamounts function as oases for microbiomes, with average moderate to high levels of microbial abundance, richness, and diversity, and they harbor distinct microbial communities. The distinct characteristics of different seamounts provide a high level of habitat heterogeneity, resulting in the wide range of microbial community diversity observed across all seamounts. Using dormant thermospores as tracers to study the effect of dispersal by ocean currents, the observed distance-decay biogeography across different seamounts shaped simultaneously by the seamounts' naturally occurring heterogeneous habitat and the limitation of ocean current dispersal was found. We also established a framework that links initial community assembly with successional dynamics in seamounts. Seamounts provide resource-rich and dynamic environments, which leads to a dominance of stochasticity during initial community establishment in surface sediments. However, a progressive increase in deterministic environmental selection, correlated with resource depletion in subsurface sediments, leads to the selective growth of rare species of surface sediment communities in shaping the subsurface community. Overall, the study indicates that seamounts are a previously ignored oasis in the deep sea. This study also provides a case study for understanding the microbial ecology in globally widespread seamounts. IMPORTANCE Although there are approximately 25 million seamounts in the ocean, surprisingly little is known about seamount microbial ecology. We provide evidence that seamounts are island-like habitats harboring microbial communities distinct from those of nonseamount habitats, and they exhibit a distance-decay pattern. Environmental selection and dispersal limitation simultaneously shape the observed biogeography. Coupling empirical data with a null mode revealed a shift in the type and strength, which controls microbial community assembly and succession from the seamount surface to the subsurface sediments as follows: (i) community assembly is initially primarily driven by stochastic processes such as dispersal limitation, and (ii) changes in the subsurface environment progressively increase the importance of environmental selection. This case study contributes to the mechanistic understanding essential for a predictive microbial ecology of seamounts.

Black Carbon in Deep-Sea Seamount Sediment Cores: Vertical Variation and Non-negligible Char Black Carbon.

Deep-sea sediments (>1000 m) are often considered to be the ultimate sink for black carbon (BC), and the long-term buried BC in these sediments is believed to potentially provide a negative feedback effect on climate warming. The burial flux of BC in marine sediments is predominantly estimated based on soot BC (SBC) in most studies, frequently ignoring the contribution of char BC (CBC). While this methodology may result in an underestimation of the BC burial flux, the precise extent of this underestimation is yet to be determined. This study used the benzene poly(carboxylic acid) (BPCA) method and chemothermal oxidation (CTO) method to analyze CBC and SBC in four deep-sea sediment cores from the Zhongnan seamount in the South China Sea, respectively. The CBC content increased from 0.026 ± 0.010% at the seamount upper part (1432 m) to 0.039 ± 0.012% at the seamount foot (4278 m), constituting approximately 25 to 42% of the SBC content. The content disparity between CBC and SBC diminishes as depth increases. In deep-sea sediments, biogeochemical factors influence the variation of CBC molecules with depth. In the seamount middle-upper part (1432 and 2465 m), highly condensed CBC gradually accumulated along the core downward profile. In the sediment core profile of the seamount middle-lower part (3497 m), benzenetricarboxylic acid and benzenetetracarboxylic acid content decreased while the BC condensation degree rose, i.e., less condensed CBC was preferentially consumed. Afterward, CBC molecules reached a relatively stable state at the seamount foot. This study reveals that CBC possesses the capacity for long-term carbon sequestration in deep-sea sediments, and its content is not negligible.

New Polyketide and Sesquiterpenoid Derivatives from the Magellan Seamount-Derived Fungus Penicillium rubens AS-130.

Rubenpolyketone A (1), a polyketide featuring a new carbon skeleton having cyclohexenone condensed with a methyl octenone chain and a new linear sesquiterpenoid, chermesiterpenoid D (2), together with seven known secondary metabolites (3-9) were isolated and identified from the Magellan Seamount-derived fungus Penicillium rubens AS-130. Their structures were determined based on detailed analysis of NMR and mass spectroscopic data and the absolute configurations of these two new compounds were elucidated by the combination of quantum mechanical (QM)-NMR and time-dependent density functional (TDDFT) ECD calculation approaches. Chermesiterpenoids B (3) and C (4) showed potent inhibitory activities against the aquatic pathogen Vibrio anguillarum with MIC values of 0.5 and 1 µg/mL, respectively, while chermesin F (6) exhibited activity against Escherichia coli with MIC value of 1 µg/mL.

Phylogeography of Colpomenia sinuosa (Ectocarpales, Phaeophyceae) along the Brazilian coast.

Colpomenia sinuosa is a cosmopolitan brown macroalgal species complex and hence a great candidate for evolutionary studies in the marine environment. Since 2009, three major C. sinuosa phylogenetic lineages, subdivided into eight subgroups, have been identified based on cox3 DNA sequences from worldwide collections. However, worldwide sampling remains limited and spotty. To date molecular data from Brazilian C. sinuosa populations have been limited to 10 specimens collected in a single locality. Nonetheless, C. sinuosa populations occur along the entire ~8,000 km Brazilian coast. Consequently, knowledge on population genetic diversity and spatial genetic structuring along most of the Brazilian coastline is nonexistent. To fulfill this gap in knowledge, we performed a phylogeographic analysis of C. sinuosa populations in Brazil. The highly variable cox3 marker was sequenced for 148 individuals collected in 12 localities in Brazil. Results identified two genetically distinct population groups (north vs. south) separated at 20.5° S latitude. Genetic diversity in northern populations is 14.6 and 15.5 times greater than southern populations in terms of haplotype and nucleotide diversity, respectively. Among northern populations, the Bahia state holds the largest genetic diversity. The southern populations had lower genetic diversity and no internal genetic sub-structure suggesting past bottlenecks followed by recent colonization from northern haplotypes. Our results do not indicate recent introductions of foreign haplotypes in Brazil and reinforce the crucial importance of historical and extant allopatric, parapatric, and sympatric processes driving marine macroalgal evolution in the Southwestern Atlantic Ocean.

Assessment of the Seafloor Topography Accuracy in the Emperor Seamount Chain by Ship-Based Water Depth Data and Satellite-Based Gravity Data.

The seafloor topography estimation is very important, while the bathymetry data and gravity data are scarce and uneven, which results in large errors in the inversion of the seafloor topography. In this paper, in order to reduce the influence of errors and improve the accuracy of seafloor inversion, the influence of different resolution data on the inversion topography in the Emperor Seamount Chain are investigated by combining ship water depth data and satellite gravity anomaly data released by SIO V29.1. Through the comparison of different resolution models, it is found that the choice of resolution affects the accuracy of the inversion terrain model. An external comparison is presented by using the international high-precision topography data and check points observations. The results show that with the increase in resolution, the fitting residuals obtained by the scale factor are optimized, and the precision of the terrain model is gradually approaching the S&S V19.1 and GEBCO-2020 models, but is better than the ETOPO1 and SRTM 30 models. By external validation using the check points, the standard deviation of the difference was reduced from 58.92 m to 47.01 m, and the correlation between the inverted terrain and the NGDC grid model was increased from 0.9545 to 0.9953. For recovering the Emperor Seamount Chain terrain, the relative error was gradually decreased with the improvement of resolution. The maximum relative error is reduced from 1.09 of 2' topography to 0.74 of 10″ topography, and the average error is reduced from 0.04 to 0.01 with an improvement by 32.11%. The terrain error between the inverted terrain model and the NGDC grid model is gradually reduced, while the error percentage is increasing by 25.51% and 21.49% in the range of -50 to 50 m and -100 to 100 m, respectively. Furthermore, the sparse area can effectively reduce the terrain standard deviation and improve the terrain correlation by increasing the resolution through the analysis of different density subsets. The error was decreased most significantly in sparse and dense homogeneous regions with increasing resolution.

Geothermobacter hydrogeniphilus sp. nov., a mesophilic, iron(III)-reducing bacterium from seafloor/subseafloor environments in the Pacific Ocean, and emended description of the genus Geothermobacter.

A novel mesophilic, anaerobic, mixotrophic bacterium, with designated strains EPR-MT and HR-1, was isolated from a semi-extinct hydrothermal vent at the East Pacific Rise and from an Fe-mat at Lo'ihi Seamount, respectively. The cells were Gram-negative, pleomorphic rods of about 2.0 µm in length and 0.5 µm in width. Strain EPR-MT grew between 25 and 45 °C (optimum, 37.5-40 °C), 10 and 50 g l-1 NaCl (optimum, 15-20 g l-1) and pH 5.5 and 8.6 (optimum, pH 6.4). Strain HR-1 grew between 20 and 45 °C (optimum, 37.5-40 °C), 10 and 50 g l-1 NaCl (optimum, 15-25 g l-1) and pH 5.5 and 8.6 (optimum, pH 6.4). Shortest generation times with H2 as the primary electron donor, CO2 as the carbon source and ferric citrate as terminal electron acceptor were 6.7 and 5.5 h for EPR-MT and HR-1, respectively. Fe(OH)3, MnO2, AsO4 3-, SO4 2-, SeO4 2-, S2O3 2-, S0 and NO3 - were also used as terminal electron acceptors. Acetate, yeast extract, formate, lactate, tryptone and Casamino acids also served as both electron donors and carbon sources. G+C content of the genomic DNA was 59.4 mol% for strain EPR-MT and 59.2 mol% for strain HR-1. Phylogenetic and phylogenomic analyses indicated that both strains were closely related to each other and to Geothermobacter ehrlichii, within the class δ-Proteobacteria (now within the class Desulfuromonadia). Based on phylogenetic and phylogenomic analyses in addition to physiological and biochemical characteristics, both strains were found to represent a novel species within the genus Geothermobacter, for which the name Geothermobacter hydrogeniphilus sp. nov. is proposed. Geothermobacter hydrogeniphilus is represented by type strain EPR-MT (=JCM 32109T=KCTC 15831T=ATCC TSD-173T) and strain HR-1 (=JCM 32110=KCTC 15832).

Seabed mining could come at a high price for a unique fauna.

The deep seafloor is teeming with life, most of which remains poorly known to science. It also constitutes an important reserve of natural resources, particularly minerals, that mining companies will start harvesting in the next few years (Nat Rev Earth Environ, 1, 2020, 158). In this context, broad biodiversity assessments of deep-sea ecosystems are urgently needed to establish a baseline prior to mining. However, significant gaps in our taxonomic knowledge and the high cost of sampling in the deep sea limit the effectiveness of conventional morphology-based surveys. In this issue of Molecular Ecology, Laroche et al. (Mol Ecol, 2020) capitalize on high throughput molecular methods to conduct one of the most detailed and rigorous surveys of the composition and biogeography of deep-seafloor metazoan communities to date. The authors show that deep seamounts in the Clarion Clipperton Zone are inhabited by rich metazoan communities that are distinct from those of the surrounding abyssal plains. These results have important conservation implications: if communities on deep seamounts were to persist after large-scale industrial mining operations on the surrounding plains, the seamounts would not serve as appropriate reservoirs to repopulate impacted areas.

Pelagihabitans pacificus gen. nov., sp. nov., a member of the family Flavobacteriaceae isolated from a deep-sea seamount.

The Gram-stain-negative, orange-pigmented, non-spore-forming, non-motile, strictly aerobic, rod-shaped bacterial strain, designated TP-CH-4T, was isolated from a seamount near the Yap Trench in the tropical western Pacific. The optimal growth conditions were determined to be at pH 7-8, 25-30 °C and in the presence of 2 % (w/v) NaCl. The major respiratory quinone was MK-6. The polar lipid profile contained phosphatidylethanolamine, two unidentified aminolipids, two unidentified phospholipids and three unidentified polar lipids. The predominant cellular fatty acids were iso-C15 : 0 and summed feature 1 (composed of C13 : 03-OH and/or iso-C15 : 1H). Phylogenetic analysis of 16S rRNA gene sequences revealed that strain TP-CH-4T was a member of the family Flavobacteriaceae and formed a distinct lineage. Strain TP-CH-4T displayed highest sequence similarities to Pseudozobellia thermophila KMM 3531T (95.1 %) and Flagellimonas flava A11T (93.9 %). Genome sequencing revealed the strain TP-CH-4T has a genome size of 4.5 Mbp and a G+C content of 44.5 mol%. Collectively, based on phenotypic, chemotaxonomic, phylogenetic and genomic evidence, strain TP-CH-4T represents a novel species of a novel genus of the family Flavobacteriaceae, for which the name Pelagihabitans pacificus gen. nov., sp. nov. is proposed. The type strain of Pelagihabitans pacificus is TP-CH-4T (=CGMCC 1.17120T=KCTC 72434T).

Algibacter pacificus sp. nov., isolated from a deep-sea seamount.

The Gram-stain-negative, rod-shaped, yellow-pigmented and facultative anaerobic bacterial strain, designated H164T, was isolated from seawater collected from the Caroline Seamounts in the Pacific Ocean. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain H164T was related to the genus Algibacter and had highest 16S rRNA gene sequence similarity to Algibacter wandonensis WS-MY22T (97.4 %). The major cellular fatty acids were iso-C15 : 0, anteiso-C15 : 0, iso-C15 : 1 G, iso-C15 : 0 3-OH and iso-C17 : 0 3-OH. The predominant menaquinone was MK-6. The polar lipid profile contained phosphatidylethanolamine, one unidentified aminolipid and two unidentified lipids. The genomic DNA G+C content of strain H164T was 33.2 mol%. The values of in silico DNA-DNA hybridization (isDDH) and average nucleotide identity (ANI) between strain H164T and A. wandonensis KCTC 32381T were 26.10 and 81.88 %. The isDDH and ANI values between strain H164T and Algibacter lectus DSM 15365T were 25.40 and 81.79 %. Combined data from phenotypic, phylogenetic, isDDH and ANI analyses demonstrated that strain H164T represents a novel species of the genus Algibacter, for which we propose the name Algibacter pacificus sp. nov. (type strain H164T=KCTC 72432T=CGMCC 1.17117T).

Flavobacterium profundi sp. nov., isolated from a deep-sea seamount.

The Gram-stain-negative, rod-shaped, facultative anaerobic, motile bacterial strain, designated TP390T, was isolated from a seamount near the Yap Trench in the tropical western Pacific. Phylogenetic analysis based on 16S rRNA gene sequence showed that strain TP390T was related to the genus Flavobacterium and had highest 16S rRNA gene sequence identity with the type strain of Flavobacterium jejuense EC11T (97.8 %). Sequence similarities to all other type strains of current species of the genus Flavobacterium were below 97 %. The predominant cellular fatty acids were iso-C15 : 0 and iso-C15 : 1G. The quinone system for strain TP390T comprised predominantly menaquinone MK-6 and the polar lipid profile contained phosphatidylethanolamine, four unknown aminolipids, one glycolipid and six unknown polar lipids. The genomic DNA G+C content of strain TP390T was 31.2 mol%. In addition, the maximum values of in silico DNA-DNA hybridization (isDDH) and average nucleotide identity (ANI) between strain TP390T with F. jejuense KCTC 42149T were 22.60 and 80.01% respectively. Combined data from phenotypic, phylogenetic, isDDH and ANI data demonstrated that the strain TP390T is representative of a novel species of the genus Flavobacterium, for which we propose the name Flavobacterium profundi sp. nov. (type strain TP390T=KACC 18559T=CGMCC 1.15398T).

Vibrio profundi sp. nov., isolated from a deep-sea seamount.

A Gram-stain negative, rod-shaped, facultative anaerobic, motile bacterial strain, designated TP187T, was isolated from a seamount near the Yap Trench in the tropical western Pacific. Phylogenetic analysis based on the 16S rRNA gene sequence showed that strain TP187T is related to members of the genus Vibrio and has high 16S rRNA gene sequence similarity with the type strains of Vibrio chagasii (97.3%) and Vibrio gallaecicus (97.1%). Sequence similarities to all other type strains of current species of the genus Vibrio were below 97%. The polar lipids profile was found to contain diphosphatidylglycerol, phosphatidylglycerol, an aminophospholipid, two aminolipids, four phospholipids and eleven unidentified polar lipids. Ubiquinone Q-8 was detected as the predominant quinone. The genomic DNA G + C content of strain TP187T was determined to be 43.7 mol%. In addition, the maximum values of in silico DNA-DNA hybridization (isDDH) and average nucleotide identity (ANI) between strain TP187T with V. chagasii LMG 21353T were 22.40 and 77.50% respectively. Both values are below the proposed cutoff levels for species delineation, i.e. 70 and 95%, respectively. Combined data from phenotypic, phylogenetic, isDDH and ANI data demonstrated that the strain TP187T is representative of a novel species of the genus Vibrio, for which we propose the name Vibrio profundi sp. nov. (type strain TP187T = KACC 18555T = CGMCC 1.15395T).

Rheinheimera marina sp. nov., isolated from a deep-sea seamount.

A bacterial strain designated TP462T, isolated from a seamount near the Yap Trench in the tropical western Pacific, was characterized using a polyphasic taxonomic approach. Strain TP462T was found to be Gram-stain-negative, aerobic, rod-shaped and motile by means of a single polar flagellum. Growth occurred at 4-37 °C (optimum, 25-30 °C) and with 0-4.0 % NaCl (optimum, 2-3 %). Phylogenetic analysis based on 16S rRNA gene sequence showed that strain TP462T was related to the genus Rheinheimera and had the highest 16S rRNA gene sequence similarity with the type strain Rheinheimera tangshanensis JA3-B52T (96.8 %). The predominant cellular fatty acids were C17 : 1ω8c, summed feature 3 (composed of iso-C15 : 0 2-OH and/or C16 : 1ω7c) and C16 : 0. The polar lipid profile contained phosphatidylglycerol, phosphatidylethanolamine and two unidentified lipids. The genomic DNA G+C content of strain TP462T was 48.7 mol%. On the basis of the evidence presented in this study, strain TP462T represents a novel species of the genus Rheinheimera, for which we propose the name Rheinheimera marina sp. nov. (type strain TP462T=KACC 18560T=CGMCC 1.15399T).

The Biology of Seamounts: 25 Years on.

Seamounts are one of the major biomes of the global ocean. The last 25 years of research has seen considerable advances in the understanding of these ecosystems. The interactions between seamounts and steady and variable flows have now been characterised providing a better mechanistic understanding of processes influencing biology. Processes leading to upwelling, including Taylor column formation and tidal rectification, have now been defined as well as those leading to draw down of organic matter from the ocean surface to seamount summit and flanks. There is also an improved understanding of the interactions between seamounts, zooplankton and micronekton communities especially with respect to increased predation pressure in the vicinity of seamounts. Evidence has accumulated of the role of seamounts as hot spots for ocean predators including large pelagic fish, sharks, pinnipeds, cetaceans and seabirds. The complexity of benthic communities associated with seamounts is high and drivers of biodiversity are now being resolved. Claims of high endemism resulting from isolation of seamounts as islands of habitat and speciation have not been supported. However, for species characterised by low dispersal capability, such as some groups of benthic sessile or low-mobility invertebrates, low connectivity between seamount populations has been found with evidence of endemism at a local level. Threats to seamounts have increased in the last 25 years and include overfishing, destructive fishing, marine litter, direct and indirect impacts of climate change and potentially marine mining in the near future. Issues around these threats and their management are discussed.

Maribacter marinus sp. nov. isolated from a deep-sea seamount.

A Gram-stain negative, rod-shaped, aerobic strain, designated YC973T, was isolated from a seamount near the Yap Trench in the tropical western Pacific. Phylogenetic analysis based on its 16S rRNA gene sequence showed that strain YC973T is related to the genus Maribacter and has high 16S rRNA gene sequence similarity to Maribacter orientalis KMM 3947T (97.6%). The predominant cellular fatty acids were iso-C15:0, iso-C15:1 G and an unidentified fatty acid of equivalent chain-length 13.565. The polar lipid profile contained phosphatidylethanolamine and five unidentified lipids. The genomic DNA G+C content of strain YC973T was 36.1 mol%. On the basis of the evidence presented in this study, strain YC973T represents a novel species of the genus Maribacter, for which we propose the name Maribacter marinus sp. nov. (type strain YC973T = KACC 19025T = CGMCC 1.16328T).

Ponticaulis profundi sp. nov. isolated from a deep-sea seamount.

A Gram-stain negative, rod-shaped, strictly aerobic, motile bacterial strain, designated YC239T, was isolated from a seamount near the Yap Trench in the tropical western Pacific. Phylogenetic analysis based on 16S rRNA gene sequence showed that strain YC239T is related to the genus Ponticaulis and has high 16S rRNA gene sequence similarity with the type strain of Ponticaulis koreensis GSW-23T (97.9%). The predominant cellular fatty acids were C18:1ω7c, C16:0, C17:0 and C17:1ω6c. Strain YC239T had Q-10 as the predominant ubiquinone. The polar lipid profile contained phosphatidylglycerol, two unidentified aminolipids and six unidentified polar lipids. The genomic DNA G+C content of strain YC239T was 52.8 mol%. Strain YC239T shared DNA relatedness of 38% with Ponticaulis koreensis KCTC 22146T. On the basis of the evidence presented in this study, strain YC239T represents a novel species of the genus Ponticaulis, for which we propose the name Ponticaulis profundi sp. nov. (type strain YC239T = KACC 19027T = CGMCC 1.15741T).

Ciliate diversity and distribution patterns in the sediments of a seamount and adjacent abyssal plains in the tropical Western Pacific Ocean.

BACKGROUND: Benthic ciliates and the environmental factors shaping their distribution are far from being completely understood. Likewise, deep-sea systems are amongst the least understood ecosystems on Earth. In this study, using high-throughput DNA sequencing, we investigated the diversity and community composition of benthic ciliates in different sediment layers of a seamount and an adjacent abyssal plain in the tropical Western Pacific Ocean with water depths ranging between 813 m and 4566 m. Statistical analyses were used to assess shifts in ciliate communities across vertical sediment gradients and water depth. RESULTS: Nine out of 12 ciliate classes were detected in the different sediment samples, with Litostomatea accounting for the most diverse group, followed by Plagiopylea and Oligohymenophorea. The novelty of ciliate genetic diversity was extremely high, with a mean similarity of 93.25% to previously described sequences. On a sediment depth gradient, ciliate community structure was more similar within the upper sediment layers (0-1 and 9-10 cm) compared to the lower sediment layers (19-20 and 29-30 cm) at each site. Some unknown ciliate taxa which were absent from the surface sediments were found in deeper sediments layers. On a water depth gradient, the proportion of unique OTUs was between 42.2% and 54.3%, and that of OTUs shared by all sites around 14%. However, alpha diversity of the different ciliate communities was relatively stable in the surface layers along the water depth gradient, and about 78% of the ciliate OTUs retrieved from the surface layer of the shallowest site were shared with the surface layers of sites deeper than 3800 m. Correlation analyses did not reveal any significant effects of measured environmental factors on ciliate community composition and structure. CONCLUSIONS: We revealed an obvious variation in ciliate community along a sediment depth gradient in the seamount and the adjacent abyssal plain and showed that water depth is a less important factor shaping ciliate distribution in deep-sea sediments unlike observed for benthic ciliates in shallow seafloors. Additionally, an extremely high genetic novelty of ciliate diversity was found in these habitats, which points to a hot spot for the discovery of new ciliate species.

Thalassotaleaprofundi sp. nov. isolated from a deep-sea seamount.

The Gram-stain-negative, rod-shaped, strictly aerobic, motile bacterial strain, designated YM155T, was isolated from a seamount near the Yap Trench in the tropical western Pacific. Phylogenetic analysis based on 16S rRNA gene sequence showed that strain YM155T was related to the genus Thalassotalea and had highest 16S rRNA gene sequence similarities with the type strains of Thalassotalea piscium T202T (97.2 %) and Thalassotalea agariperforans M-M1T (97.2 %). The predominant cellular fatty acids were C17 : 1ω8c, summed feature 3 (composed of iso-C15 : 0 2-OH and/or C16 : 1ω7c) and iso-C16 : 0. Ubiquinone 8 (Q-8) was the respiratory quinone. The polar lipid profile contained phosphatidylglycerol, phosphatidylethanolamine, two unidentified phospholipids and one unidentified lipid. The genomic DNA G+C content of strain YM155T was 36.1 mol%. On the basis of the evidence presented in this study, strain YM155T represents a novel species of the genus Thalassotalea, for which we propose the name Thalassotalea profundi sp. nov. (type strain YM155T=KACC 18563T=CGMCC 1.15922T).

Metazoan parasite communities and diet of the velvet belly lantern shark Etmopterus spinax (Squaliformes: Etmopteridae): a comparison of two deep-sea ecosystems.

By combining an examination of stomach contents yielding a snapshot of the most recent trophic niche and the structure of parasite communities reflecting a long-term feeding niche, this study aimed at gaining more comprehensive information on the role of the small-sized deep-water velvet belly lantern shark Etmopterus spinax in the local food webs of the Galicia Bank and the canyon and valley system of the Avilés Canyon, which have been both proposed for inclusion in the Natura 2000 network of protected areas. As far as is known, this study provides the first comparative parasite infracommunity data for a deep-sea shark species. Component parasite communities in E. spinax were relatively rich, whereas the infracommunities were rather depauperate, with similar low diversity at both localities. The significant differences in the composition and structure of both parasite communities and prey assemblages indicate differential effects of the two deep-sea ecosystems on both long-term and most recent trophic niches of E. spinax. These results underline the importance of the use of multivariate analyses for the assessment of geographical variation in shark populations based on parasites and diet data.